1888-89.] Mr John Aitken on 
Dust Particles. 
171 
For measuring quantities less than 1 c.c., the “battery” of stop- 
cock M is used. The following are 
the sizes of the bores in the 
plugs of the different measures : — 
Diameter. 
Length. 
Capacity. 
Large plug, . 4 61 mm. 
15 mm. 
250 c.mm. 
Medium plug, . 2 53 mm. 
10 mm. 
50 c.mm. 
Small plug, . 1 - 27 mm. 
8 mm. 
10 c.mm. 
That is, their capacities are respectively J, and of a cubic 
centimetre, so that, in working with these measures, the number 
counted per c.c. of the air in the receiver requires to be multiplied 
by 200 for the large measure, by 1000 for the medium, and by 5000 
for the smallest measure. 
When using the portable apparatus, it is supported on a tripod 
stand. Two plans are shown in Plate IY. for doing this. Pig. 1 
shows the design first made, and fig. 2 an alteration afterwards 
adopted. In fig. 1, T is the “ head'’ of the tripod. The upper end 
of the pump is provided with a flange and a nut N, by means of 
which the apparatus is securely attached to the tripod when in use, 
but can be separated for easy carriage. The objection to this plan is, 
that the tripod legs require to be at least 4 feet long. Under most 
conditions this is no disadvantage, but, when much coach or railway 
travelling has to be done, a bundle of rods that length is a consider- 
able inconvenience. No doubt, a folding tripod might be adopted, 
but it was thought better to make the stand like a walking-stick 
3 feet long, so that it might be an assistance in walking, and at the 
same time easily packed for carriage along with umbrellas and sticks. 
In order to carry out this idea, the plan shown in fig. 2 was 
designed. A is the air-pump as before ; B is a metal support, to 
the top of which the air-pump is secured by a movable screw-joint, 
while its lower end is securely fixed to the tripod “ head ” T. The 
pump is separated from the support B when packed for travelling. 
The piston of the pump is moved by means of the collar C, which 
slides on B. The scale for the pump is placed on B, as shown at 
lower end, fig. 2. In order to bind the whole apparatus firmly 
together, one end of the tube D, fig. 2, is screwed into the lower end 
of the filter F, fig. 1, and the other end is fixed to the tripod. 
When the length of the tripod legs is no objection, the plan shown 
in fig. 1 seems to be the steadiest, whilst the other is the most 
convenient for travelling. 
